Comparison of the inhibition mechanisms of adalimumab and infliximab in treating tumor necrosis factor α-associated diseases from a molecular view

Abstract

TNFα-targeting therapy with the use of the drugs Etanercept, Infliximab, and Adalimumab is used in the clinical treatment of various inflammatory and immune diseases. Although all of these reagents function to disrupt the interaction between TNFα and its receptors, clinical investigations showed the advantages of Adalimumab treatment compared with Etanercept and Infliximab. However, the underlying molecular mechanism of action of Adalimumab remains unclear. In our previous work, we presented structural data on how Infliximab binds with the E-F loop of TNFα and functions as a TNFα receptor-binding blocker. To further elucidate the variations between TNFα inhibitors, we solved the crystal structure of TNFα in complex with Adalimumab Fab. The structural observation and the mutagenesis analysis provided direct evidence for identifying the Adalimumab epitope on TNFα and revealed the mechanism of Adalimumab inhibition of TNFα by occupying the TNFα receptor-binding site. The larger antigen-antibody interface in TNFα Adalimumab also provided information at a molecular level for further understanding the clinical advantages of Adalimumab therapy compared with Infliximab.

Keywords: Adalimumab; Antibodies; Autoimmune Diseases; Crystal Structure; Epitope; Mechanism; Protein Targeting; Tumor Necrosis Factor (TNF).

FIGURE 1.

Overall structure of the TNFα-Adalimumab Fab complex. The TNFα-Adalimumab Fab complex is shown as ribbon diagrams in two orientations: top view, looking down the crystallographic 3-fold symmetry axis; side view, with the crystallographic 3-fold axis vertical (middle). The central TNFα molecules are colored green, blue, and cyan, respectively; the light chain and heavy chain of the Adalimumab Fab are colored yellow and red, respectively.

FIGURE 2.

Structural variations of TNFα in free form and complex forms. A single subunit of the TNFα trimer in the free form or complex forms of the TNFα-Infliximab Fab, the Adalimumab Fab, and TNFR2 are shown. The free state of the TNFα molecule is colored orange, whereas complex states with Infliximab Fab, Adalimumab Fab, and TNFR2 are colored pale green, red, and light blue, respectively.

FIGURE 3.

The TNFα-Adalimumab Fab interface. A, surface representations of the Adalimumab Fab (left) and the TNFα-Adalimumab Fab complex (right) and ribbon diagrams corresponding to the surfaces shown above with the same color scheme. The light chain and heavy chains of the Adalimumab Fab are colored yellow and red, respectively, whereas TNFα molecules are colored green, blue, and cyan. Contact surfaces are highlighted in blue on Adalimumab and red on TNFα. B, stereo view of the detailed TNFα-Adalimumab Fab interface. The residues that are involved in the intermolecular interaction are shown as colored sticks with the same scheme as the surface representation above; the Adalimumab Fab and TNFα molecules are presented as ribbon diagrams. Dashed lines denote hydrogen bonds.

FIGURE 4.

A stereo view of the epitope density map in the TNFα-Adalimumab Fab binding interface. The omit map of the epitope on the TNFα polypeptide is contoured at 1.0 σ. The TNFα molecule is shown as a white cartoon, whereas the epitope is represented as colored sticks.

FIGURE 5.

A comparison of the interface between TNFα and receptors and Infliximab/Adalimumab Fab complexes. A comparison of the interface between TNFα and receptors and mAbs is shown. TNFα from the complex structures is represented as a colored surface with TNFR2 and the mAb Fabs interface highlighted in red at one of three interfaces on the TNFα trimer. The E-F loop region, which is missing in the TNFα-TNFR2 (A) complex because of a lack of interaction, is labeled. The TNFβ from the TNFβ-TNFR1 (B) complex structure is shown as a colored surface with one of the TNFR1-binding sites highlighted in red. The TNFα-Infliximab Fab (C) and the TNFα-Adalimumab Fab (D) interfaces are shown as colored surfaces with TNFα-binding sites highlighted in red.

FIGURE 6.

Sequence comparison between two TNFα therapeutic antibodies (Infliximab and Adalimumab). The CDRs are highlighted by black frames and labeled. The residues that play crucial roles in the antibody-antigen interaction are framed with blue frames. The residue numbers (top) refer to those in Infliximab.